[tip:x86/urgent] x86/a.out: Clear the dump structure initially

[tip-bot for Borislav Petkov]

Commit-ID:  10970e1b4be9c74fce8ab6e3c34a7d718f063f2c
Gitweb:     https://git.kernel.org/tip/10970e1b4be9c74fce8ab6e3c34a7d718f063f2c
Author:     Borislav Petkov <bp@xxxxxxx>
AuthorDate: Tue, 12 Feb 2019 14:28:03 +0100
Committer:  Borislav Petkov <bp@xxxxxxx>
CommitDate: Wed, 13 Feb 2019 12:10:51 +0100

x86/a.out: Clear the dump structure initially

dump_thread32() in aout_core_dump() does not clear the user32 structure
allocated on the stack as the first thing on function entry.

As a result, the dump.u_comm, dump.u_ar0 and dump.signal which get
assigned before the clearing, get overwritten.

Rename that function to fill_dump() to make it clear what it does and
call it first thing.

This was caught while staring at a patch by Derek Robson
<robsonde@xxxxxxxxx>.

Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Cc: Derek Robson <robsonde@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Michael Matz <matz@xxxxxxx>
Cc: x86@xxxxxxxxxx
Cc: <stable@xxxxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/20190202005512.3144-1-robsonde@xxxxxxxxx
---
 arch/x86/ia32/ia32_aout.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/ia32/ia32_aout.c b/arch/x86/ia32/ia32_aout.c
index f65b78d32f5e..7dbbe9ffda17 100644
--- a/arch/x86/ia32/ia32_aout.c
+++ b/arch/x86/ia32/ia32_aout.c
@@ -51,7 +51,7 @@ static unsigned long get_dr(int n)
 /*
  * fill in the user structure for a core dump..
  */
-static void dump_thread32(struct pt_regs *regs, struct user32 *dump)
+static void fill_dump(struct pt_regs *regs, struct user32 *dump)
 {
 	u32 fs, gs;
 	memset(dump, 0, sizeof(*dump));
@@ -157,10 +157,12 @@ static int aout_core_dump(struct coredump_params *cprm)
 	fs = get_fs();
 	set_fs(KERNEL_DS);
 	has_dumped = 1;
+
+	fill_dump(cprm->regs, &dump);
+
 	strncpy(dump.u_comm, current->comm, sizeof(current->comm));
 	dump.u_ar0 = offsetof(struct user32, regs);
 	dump.signal = cprm->siginfo->si_signo;
-	dump_thread32(cprm->regs, &dump);
 
 	/*
 	 * If the size of the dump file exceeds the rlimit, then see